That doesn't work as well as the Bussard Collectors.

A highly fictionalized variation of this concept, called the Bussard Hydrogen Collector or Bussard Ramscoop appears in the Star Trek saga as part of the matter/antimatter propulsion system that allows Starfleet ships to travel faster than the speed of light. In the saga, the ramscoops attach to the front of the warp nacelles, where (when the ship's internal supply of deuterium runs critically low) they collect interstellar hydrogen and convert it to deuterium and anti-deuterium for use as the primary fuel in a starship's warp drive.